This application relates to tandem compressors that share a common suction manifold and a common discharge manifold. A common intermediate pressure manifold is connected to an intermediate port in each compressor such that a working fluid at some intermediate pressure can be directed to the compression chambers, or taken away from the compression chambers, of both compressors. This application particularly applies to open-cycle systems. In these systems, as compared to closed-cycle systems (such as typical refrigerant systems), an external source supplies working fluid to the compressor suction or intermediate port. The fluid that leaves the discharge port does not return to the suction port (or may come back to the suction port only indirectly, after passing through some other process application). This arrangement would be typical, for example, of natural gas applications, where a natural gas is pumped from a supply tank to be burnt in a number of industrial applications.
Compressors are used in various applications. In some applications, compressors may be utilized to compress air, or to move process gas, such as, for example, a hydrocarbon gas. One technique that is known in the compressor art is the use of “tandem” compressor configurations. Tandem compressor arrangements include at least two compressors that operate in parallel that can be controlled individually or simultaneously. A fluid to be compressed is typically directed through a common suction manifold and then into suction ports associated with each compressor. The compressors independently compress the working fluid and pass it downstream to individual discharge ports, and then typically to a common discharge manifold.
Tandem compressors are operable to deliver compressed gas, and in some cases, various amounts of compressed gas, depending on the demand. As an example, one or more compressors may be taken offline to reduce the amount of gas delivery. Tandem compressors may be of different sizes to provide more flexibility in the amount of gas delivered.
Another technique known in the art is the use of intermediate pressure ports in a compressor. As one example, an intermediate port may receive a fluid at an intermediate (between suction and discharge) pressure to be directed into the compression chambers at an intermediate point in the compression process. This technique can be utilized for cooling the compressor components and lowering a discharge temperature of the compressed working fluid. In other applications, a working fluid may flow from intermediate pressure ports back to the suction line to reduce the amount of the working fluid being compressed by the compressor and delivered to the discharge port. This technique is known as “unloading” of the compressors.
In other designs, an intermediate pressure fluid may be tapped from the intermediate port in the compressor and utilized at any downstream location requiring a compressed gas at a lower pressure than the higher discharge pressure.
While the above applications of having tandem compressors with intermediate ports are known to be utilized for closed-loop refrigerant systems, especially in conjunction with the use of an economized cycle to increase the system capacity and efficiency; the above-described applications of having a combination of intermediate pressure ports and tandem compressors with common manifolds have not been utilized in the open compression cycles, or applications where the compressed discharged fluid doesn't directly return to a suction manifold of the tandem compressors.